1. Field of the Invention
The present invention relates to improvements in the art of reducing iron oxide such as iron ore by heating with use of a carbonaceous reductant such as coke to produce metallic iron. More specifically, the present invention relates to an improved method which is capable of efficiently reducing iron oxide into metallic iron by a simplified treatment while efficiently separating slag forming components included as gangue in iron ore and the like from metallic iron in the form of slag, thereby obtaining high-purity granular metallic iron in a high yield.
The present invention also relates to a method of producing metallic iron, which is improved to ensure a stabilized continuous production by lessening damage to hearth refractories that is a problem in producing metallic iron from a formed raw material comprising a carbonaceous reductant and a substance containing iron oxide with use of a moving hearth type reduction melting furnace.
The present invention further relates to an improved feed device for efficiently supplying auxiliary raw materials such as an atmosphere adjusting agent onto the hearth of a moving hearth type reduction melting furnace.
2. Description of the Related Art
The shaft kiln process, a representative of which is the Midrex process, is conventionally known as a direct ironmaking method for obtaining reduced iron by directly reducing an iron oxide source such as iron ore or iron oxide with use of a carbon material or a reducing gas. According to the direct ironmaking method of this type, a reducing gas prepared from natural gas is blown into the furnace through a tuyere opening defined in a lower portion of the shaft kiln, and iron oxide is reduced into metallic iron by the reducing power of the reducing gas. Attention has recently been directed to another reduced iron producing process which uses a carbon material such as coal instead of natural gas as a reducing agent, and one such process, what is called xe2x80x9cSL/RNxe2x80x9d process, has already been put to practice.
U.S. Pat. No. 3,443,931 discloses another process wherein a carbon material and powdery iron oxide are mixed together and formed into a mass or a pellet, which in turn is subjected to reduction by heating on a rotary hearth to produce reduced iron.
U.S. Pat. No. 5,885,521 discloses a technique wherein a granular raw material of reduced iron dried in a drying furnace is supplied to the hearth through a supply pipe extending through a ceiling portion of a moving hearth type furnace down to a location adjacent the hearth, and the layer thickness of the granular raw material of reduced iron is primarily adjusted with a pellet leveler provided on a side face of the leading end of the supply pipe and then further adjusted with a smoother provided downstream of the pellet leveler in the moving direction of the hearth.
Also, a melting reduction process such as the DIOS process is known as a process for directly reducing iron oxide into reduced iron. According to this process, iron oxide is previously reduced to a reduction rate of about 30%, and thereafter such iron oxide is directly subjected to a reduction reaction with carbon in an iron bath until iron oxide is turned into metallic iron.
Japanese Patent Laid-Open Gazette No. HEI 8-27507 discloses another direct reduction ironmaking process wherein a layer of a carbonaceous reductant powder containing a desulfurizing agent and a layer of iron oxide powder are stacked on each other on a moving hearth and the stack thus formed is heated to obtain sponge iron.
Japanese Patent Laid-Open Gazette No. HEI 11-106812 discloses a technique wherein a raw material comprising iron ore and a solid reducing agent supplied into a rotary hearth type furnace (reducing furnace) through a pipe-shaped charging bore extending through a ceiling portion of the furnace is passed on a partition wall to the hearth, and the hearth bearing the raw material is moved to allow the raw material to be reduced during one round within the furnace and then ejected. This technique is particularly characterized that high-temperature ore having been reduced is laid under the partition wall to preheat the raw material on the partition wall by utilizing radiant heat from the reduced ore, while the reduced ore of which the temperature is lowered is ejected through an ejection port.
The inventors of the present invention have been making a study for a long time to develop a technique which is capable of efficiently obtaining metallic iron having a high iron purity from iron ore having a relatively low content of iron as well as from iron oxide having a higher content of iron by a simplified treatment. The following method, developed as a result of the study, was formerly proposed in Japanese Patent Laid-Open Gazette No. HEI 9-256017.
This method is characterized that in the production of metallic iron by reducing a formed body comprising a carbonaceous reductant and iron oxide by heating, the iron oxide is reduced in a solid state by heating to form and grow a metallic iron skin, the reduction by heat is continued until iron oxide is no longer present inside, and heating is further continued to cause slag produced inside to flow out of the metallic iron skin thereby separating metallic iron and slag from each other.
According to one aspect of the present invention, there is provided a method of producing granular metallic iron, comprising: heating a formed raw material comprising a carbonaceous reductant and a substance containing iron oxide in a reduction melting furnace to subject the iron oxide contained in the formed raw material to solid-state reduction; and carburizing reduced iron resulting from the solid-state reduction with carbon contained in the carbonaceous reductant to cause the reduced iron to melt, while separating off gangue components contained in the formed raw material and causing resulting molten metallic iron to coalesce into the granular metallic iron, wherein an atmospheric gas present in proximity to the formed raw material in the caburizing and melting step has a reduction degree of not less than 0.5.
According to another aspect of the present invention, there is provided a method of producing metallic iron, comprising forming a deposit layer containing slag produced in a reduction melting process on hearth refractories, thereby protecting the hearth refractories while producing the metallic iron.
According to yet another aspect of the present invention, there is provided a device for supplying a raw material or an auxiliary raw material to a hearth of a moving hearth type reduction melting furnace adapted to produce metallic iron, the device comprising a supplying duct vertically connecting with a ceiling portion of the furnace.
These and other features and attendant advantages of the present invention will become apparent from the reading of the following detailed description with reference to the attached drawings.